Chief Justice John Roberts changed his mind midway through deliberations to uphold the Affordable Care Act -- commonly known as Obamacare -- in the U.S. Supreme Court, a betrayal that allegedly led the court's fellow conservatives to leak Roberts' change of heart to the media.

That's according to excerpts from Jeffrey Toobin's "The Oath: The Obama White House and the Supreme Court," which was leaked to Politico's Playbook this week. In the book Toobin, a New Yorker writer and CNN legal analyst, reports that Roberts clashed with Justice Antonin Scalia after the chief justice was unable to find middle ground with court conservatives and strike down the health care law.

Roberts had initially intended to side with the conservatives to overturn the law, according to the book, but reportedly hesitated after considering the implications such a ruling would have on his legacy.

"Roberts was a conservative and lifelong partisan Republican. ... Roberts had dual goals for his tenure as chief justice - to push his own ideological agenda but also to preserve the court's place as a respected final arbiter of the nation's disputes," Toobin wrote, according to Politico. "A complete nullification of the health care law on the eve of a presidential election would put the court at the center of the campaign ... Democrats, and perhaps Obama himself, would crusade against the court, eroding its moral if not its legal authority. ... Gradually, then with more urgency, Roberts began looking for a way out."

In his majority opinion, Roberts ultimately concluded the law's individual mandate fell within Congress' power to collect taxes, thus making it constitutional. The law was upheld in a 5 to 4 vote, with the liberal justices backing it on different grounds.

According to Toobin, the court's conservatives and their law clerks were "so outraged that Roberts might betray them" that someone leaked news of his switch soon after the decision was made.

"The four conservatives had overplayed their hand with the chief justice," he writes. "By demanding that Roberts kill off the entire health care law, they prompted him to look for some kind of middle ground. ... Scalia was enraged at the chief. ... With all the changes, the cross-references among the various opinions became confused," Toobin wrote.

Scalia insists, publicly, that he and Roberts never feuded over the health care decision.

"You should not believe what you read about the court in the newspapers," Scalia told CNN'S Piers Morgan. "Because the information has either been made up or given to the newspapers by somebody who is violating a confidence, which means that person is not reliable."